The present invention generally relates to systems and methods of purge valve flow control for use with evaporative emissions control systems, and particularly relates to systems and methods for determining purge valve flow tolerance.
Variable flow rate purge valves used in evaporative emissions control systems suffer from problems relating to part-to-part tolerance. For example, flow rate at low duty cycle can vary from part-to-part by as much as three-hundred percent, resulting in serious drivability issues at low engine speeds, especially with smaller displacement engines. As a result, past evaporative emissions control systems have not been able to utilize less expensive purge valves with less demanding part-to-part tolerance. As a further result, other solutions have focused on utilizing constant flow rate purge valves to avoid the tolerance issue.
What is needed is a solution that allows evaporative emissions control systems to utilize less expensive purge valves with less demanding part-to-part tolerance. Thus, the need remains for an adaptive system and method of purge valve control that is capable of determining purge valve tolerance and operating accordingly. The present invention fulfills this need.
In one aspect of the invention, a method for determining purge valve flow tolerance for use with evaporative emissions control systems includes developing an equation based on data relating purge valve duty cycle to flow, wherein the equation describes a flow curve with reference to a first axis and a second axis. The method further includes using the equation as a base equation for flow, and adapting the equation for part-to-part tolerance as a function of an intercept point of the equation with respect to the first axis, wherein the first axis relates to duty cycle.
In another aspect of the invention, a purge valve flow tolerance determination system for use with evaporative emissions control systems includes a memory storing an equation based on data relating purge valve duty cycle to flow, wherein the equation describes a flow curve with reference to a first axis and a second axis. A purge valve operation module is adapted to operate a purge valve based on the equation. An adaptation module adapts the equation for part-to-part tolerance as a function of an intercept point of the equation with respect to the first axis, wherein the first axis relates to duty cycle.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.